It is known to use lithium bis(fluorosulfonyl)imides as salts for the electrolyte in various electrochemical devices, especially in batteries. The compounds that are the most representative are compounds of the type (RFSO2)2NM in which RF is a perfluoroalkyl group and M is an alkali metal cation or organic cation. These compounds have properties that are relatively good but that are however insufficient.
It is known to prepare sulfonylimides [RSO2NSO2R′]M by reaction of a sulfonyl fluoride RSO2F with a sulfonamide R′SO2NH2. However, the condensation reaction is in competition with a hydrolysis and the sulfonylimide is obtained with a low yield. Moreover, it is very difficult to modify the R group which has an electron-withdrawing nature (with a view to giving it additional properties, enabling for example grafting or polymerization) without degrading the sulfonimide group.